Honeycomb sandwich panels are widely used as structural materials in aircraft, sports goods, marine structures, vehicles, and the like because of their lightness and rigidity. In particular, panels for aircraft interior parts are produced by impregnating a reinforcing fibrous base with an epoxy matrix resin to prepare prepregs, laminating the prepregs on a honeycomb core, and heating the laminate under pressure.
Regulations providing fuming properties of aircraft interior parts have recently been laid down and enforced by the Federal Aviation Administration, U.S.A. (F.A.A.) from the standpoint of safety assurance for passengers in the case of fire, and structural materials having low fuming characteristics on burning have been reguired.
Phenolic resins are essentially flame retardant and low fuming. However, when used as a surfacing material of honeycomb sandwich panels, phenolic resins are very brittle and poor in self-adhesion.